Major Customers (Details) (USD $) In Thousands, unless otherwise specified			6 Months Ended
Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 NRG Energy, Inc. (fka GenOn Energy, Inc.) [Member]	Jun. 30, 2012 NRG Energy, Inc. (fka GenOn Energy, Inc.) [Member]	Jun. 30, 2012 Indiana Harbor Coke Company, L.P. [Member]	Jun. 30, 2012 PPL Corporation [Member]	Jun. 30, 2013 American Electric Power Company, Inc. [Member]
Revenue, Major Customer [Line Items]
Receivable balance	$ 24,693	$ 33,560	$ 2,862				$ 2,501
Sales			$ 22,948	$ 19,365	$ 19,657	$ 21,082	$ 17,972

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.3-4)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 3

-Subparagraph a(1)

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 4

-Article 5

Name:	us-gaap_AccountsReceivableNetCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant